Powered snowthrowers are well known and are generally either single stage or two stage. Single stage snowthrowers are so named because they have only one powered implement, namely the impeller, for both picking up and throwing the snow outwardly away from the snowthrower. Two stage snowthrowers, on the other hand, utilize two separate means for consecutively handling the snow, typically an auger for picking up the snow and a high speed fan for throwing the snow away from the snowthrower. Both types of snowthrowers have their own particular advantages and disadvantages. For example, single stage snowthrowers are generally lighter and less expensive than two stage snowthrowers, but they generally do not throw snow as far or control the direction of the thrown snow as well as do two stage snowthrowers.
Mention should also be made of so-called mid-model snowthrowers (e.g., see U.S. Pat. Nos. 4,694,594 and 4,322,896) which might be considered a cross between a single stage and a two stage. Such mid-model snowthrowers typically include opposed auger flights that feed snow to a central snowthrowing section that rotates on the same shaft as the auger flights. Importantly, mid-model snowthrowers are classified herein as single stage snowthrowers, given the fact that they indeed have only one powered implement, albeit a fairly sophisticated multi-purpose implement. The present invention relates primarily to single stage snowthrowers (including mid-model type single stage snowthrowers), and the remainder of this discussion will focus thereon.
A typical single stage snowthrower is illustrated in U.S. Pat. No. 3,359,661 to Speiser. This type of snowthrower includes a housing which is generally open in front having spaced side walls connected by a rear wall that includes an arcuate lower portion. A snowthrowing impeller is rotatably journalled between the side walls to sit in front of the lower portion of the rear wall. The impeller includes a pair of flexible radially extending paddles for picking up and throwing snow. Speiser's paddles, preferably formed from linear polyethylene, are flat and are rigidly mounted along their entire length on a shaft coupled to the snowthrower's prime mover. Elongate reinforcing brackets and threaded fasteners serve to connect the paddles to the shaft. Vanes, mounted at the top of the housing opening, selectively direct the snow thrown by the flat paddles either forwardly or to one side or the other of the snowthrower.
While the Speiser type of snowthrower is generally useful for its intended purpose, the flat paddle/vane combination generally can't throw the snow as far, or control the direction of the thrown snow as well, as a two stage snowthrower. Also, the Speiser snowthrower is susceptible to damage when it encounters an obstruction such as a rock, ice chunk or tree branch. This vulnerability is primarily attributable to the fact that the paddles, although somewhat flexible, are rigidly connected along their entire length to the rotating shaft which in turn is coupled to the prime mover by a drive train, e.g., belts and pulleys. Thus, when a foreign object or obstruction (e.g., large chunk of ice or stick) becomes wedged between the impeller and the rear wall of the housing, the latter sometimes cracks, particularly if it is made from plastic. Moreover, the impact caused by the obstruction is in effect transmitted to the prime mover by the drive train, reducing the prime mover's power, causing stalling, and shortening the useful lives of the prime mover and drive train components.
An improved single stage snowthrower (of the mid-model type) is shown and described in U.S. Pat. No. 4,694,594, to R.A. Thorud et al. The Thorud snowthrower includes a single rotating implement having a pair of opposed auger flights feeding an axially-aligned central snowthrowing section fixedly attached to the same shaft as the auger flights. Attached to the rotating shaft is a pair of opposed metal stampings which sandwich opposing radially extending flexible paddles. The paddles are curved in such a way that the auger flights smoothly blend into the central snowthrowing section. Although the Thorud device is superior to the Speiser type of snowthrower in many respects, including directional control of the thrown snow, the housing of the commercial embodiment of Thorud had to be made very strong and massive to accommodate obstruction impact without cracking. The Thorud housing is most vulnerable when the obstruction is encountered by the central snowthrowing section of the impeller since it tends to strike obstructions squarely in accordance with its more-or-less flat radial configuration. The auger sections are less likely to cause damage, since they tend to strike obstructions obliquely. Also, it was perceived that the Thorud design could or should be improved to achieve weight and cost savings.
A lightweight snowthrower is advantageous in terms of maneuverability and portability. The obstruction impact problem, therefore, is particularly troublesome, as lightweight relatively fragile plastics are frequently utilized to achieve a lightweight snowthrower. Several solutions to the impact problem have been proposed, including using resilient elements between the prime mover and the rotating impeller shaft, and/or using slip clutches or the like. See, for example, U.S. Pat. No. 4,346,526 which discloses use of a torsion bar (resilient element) coupling in a snowthrower, and U.S. Pat. No. 3,313,049 which discloses a slip clutch in the impeller drive train of a snowthrower. Although both proposed solutions are theoretically sound, they add weight, cost, and complexity to the snowthrower. Slip clutches, in particular, are susceptible to slipping at too low a torque or not slipping at all when most needed. Moreover, as discussed above the obstruction impact problem is attributable primarily to the central snowthrowing section of the impeller, and thus it is unnecessary to provide "springiness" or "slip" in the entire impeller, particularly the auger portions.
Only one prior art reference, U.S. Pat. No. 3,086,304 to Tendresse, seems to have recognized that the obstruction impact problem is most closely associated with the central snowthrowing section of an impeller, and that there is no need to provide slip clutches or the like in the impeller drive train. Tendresse discloses a snowthrower with a "self-restoring" impeller. Two end augers, mounted on a rotating shaft, feed snow inwardly to a central "impeller" comprised of a pair of 180.degree. opposed inner portions fixed to the rotating shaft and a pair of outer portions hinged thereto. Springs resist rotation of the outer portions relative to their respective inner portions, so that normally each associated pair of inner and outer impeller portions combine to form a flat snowthrowing paddle, but when an obstruction is encountered the outer portion can pivot against the resistance of the spring.
While Tendresse seems to have recognized the obstruction impact problem discussed above, his proposed solution is inadequate for several reasons. For one thing, the metal impellers, springs, hinges and associated parts make for a massive, complicated assembly. Also, Tendresse's springs and hinges would tend to ice up and become rigid in some circumstances.
The present invention, a resilient impeller for a single stage snowthrower, addresses the obstruction impact problem disclosed above. In addition, the impeller of the present invention provides cost and weight savings as compared to the prior art.